Linking nitrous oxide emissions from starch wastewater digestate amended soil to the abundance and structure of denitrifier communities

Anaerobic digestion is widely used in starch wastewater pre-treatment and can remove the COD effectively, however, the effluents are nutritious and often need supplemental aerobic treatments to remove nutrients prior to discharge. The objective of this study was to investigate the feasibility of using the liquid digestate of starch wastewater (LDSW) as a fertilizer. This pot experiment was conducted with Ipomoea aquatica Forsk in a greenhouse with six treatment groups. The crop growth was significantly promoted, while the accumulation of soil nitrate was not influenced after LDSW addition, compared to the control. In addition, at the same nitrogen input, the yield of high-LDSW treatment was 65.2%, 92.3% and 69.2% higher than those of chemical fertilizer treatment during the three growth periods. Furthermore, average N2O emission with high-LDSW addition was 15.8 g N/(ha.d), accounting for 15.0% of which under high chemical fertilizer treatment, due to the significantly enhanced denitrification genes (nirK, nirS and nosZ) abundance. Besides, the changes of soil N2O-reducing bacteria were performed by high-throughput sequencing of nosZ. Our findings suggested that LDSW had many opportunities for sustainable agriculture to guarantee high yields while reducing negative environmental impacts.